Rollout of High-Data Rate Power Line Gear Raises International Worries

The “standardization landscape” is a “quite complex issue,” said Reiner Liebler, the reporting member on PLT issues in the ITU-R group on spectrum engineering techniques. PLT poses “a theoretical threat,” said John Mettrop, chairman of the ITU-R working group on the maritime mobile, aeronautical mobile and radiodetermination services. “We need to prove whether that theory is a practical threat,” said Mettrop, who spoke about broadband PLT.

Aeronautical interests have “total reliance” on automated systems used in bands being “looked at” by PLT, Mettrop said. Aeronautical interests look to resolve interference before it’s an issue, he said. Ofcom U.K. has taken a view to work “proportionately” on interference depending on how many complaints are made, he said.

Some aeronautical systems use HF and VHF bands, navigation services and in the future possibly future surveillance systems across the whole range below 500 MHz, Mettrop said. “We are talking about safety of life,” he said. Desired reliability is extremely high, he said. PLT “probably” won’t have too much impact below 30 MHz, he said. Frequencies above about 100 MHz are a concern, he said.

Changes in U.K. building practices include using metal-backed insulation on walls may help stem emissions, but not those going through the roof, Mettrop said. That means interference toward the sky may be significant, he said referring also to the lack of insulation and resulting increased interference through the tops of “biscuit ovens” and “RF heaters."

An Ofcom U.K.-commissioned study showed the probability of HF interference using power control as a mitigation technique at greater then 20 percent, Mettrop said, and less than 1 percent using power control and notching. The study showed a greater than 20 percent probability of interference for the VHF instrument landing system with no mitigation and less than 1 percent with notching, he said. Those numbers would require closing airports, he said.

There are “forces” that are willing to “simply pollute” the RF environment, said Charles Einolf, representing two ITU-R broadcasting groups, referring to devices using power lines for electrical power management and for high speed data communications. PLT devices are despoiling 14 broadcast allocations in the HF band, said Einolf, who works for CBS Broadcasting. PLT devices come in two varieties, Einolf said. He cited an access device using nearby power lines and intended to bring high speed data into the home, and localized devices, which are more common and are readily available for in premises broadband data links. A single device or a system using PLT could easily “wipe out” the entire HF, VHF and portions of UHF band, he said.

Some manufacturers have increased the bandwidth of devices, Einolf said. Peak values during data transfer and idle modes measured by the “IRT laboratory” showed that a device claimed as compliant with the ITU-T recommendation G.9960 exceeded CISPR limits by more than 20 dB, Einolf said. The recommendation is on the system architecture and physical layer specification for “unified high-speed wire-line based home networking transceivers."

The device, a “Belkin Gigabit Powerline HD, identified as Mediaxtream” was “certainly not a G.9960 modem,” said Les Brown, the associate reporting ITU-T member for work on transceivers for customer access and in-premises networking systems on metallic conductors. “We're doing all our effort trying to work with ITU-R to address emissions issues, and I think this gives a very bad message to the industry about G.9960,” said Brown, who works for semiconductor company Lantiq. Brown asked for the information to be removed from broadcaster’s presentation. Information from the IRT study was taken from a submission to ITU-R groups, Einolf said. Einolf didn’t respond to our request for the study. Access to ITU documents is restricted to members.

The “problem” is universal, involving ITU and its relationship with other standards organizations, Einolf said. It’s not simply an ITU-R or ITU-T problem, he said. ITU, administrations and other standards development organizations must commit to work to ensure PLT devices will operate “without further pollution of the RF environment,” Einolf said.

The radio astronomy band near 25 MHz is “completely masked” using an antenna 46 meters away from a test site with a high definition power line communications device, said Masatoshi Ohishi, representing ITU-R groups dealing with science services, referring to a study in Japan. Antennae up to 126 meters away were also tested, he said. Comparisons of emissions to calculated protection criteria showed “too much” interference, said Ohishi, who works for Japan’s National Astronomical Observatory.

Computer processing techniques can’t be used to subtract PLT noise, Ohishi said. Calculated separation distances between a single radio astronomy antenna and two PLT modems would be 33 km., he said. Exclusion zones at any HF radio astronomy station are impractical, he said referring to the non-licensed use of the devices. “Nobody can manage PLT modem locations,” he said.

"Permanent notches” to the radio astronomy bands are “the only way and the best way to protect the radio astronomy service,” Ohishi said. The depth of the notches may need to be 50 dB, he said.

Notches fill up, said Peter Chadwick, an expert consultant for the International Amateur Radio Union citing a 2010 IARU submission to an ITU-R working party on spectrum engineering techniques. Measurements have shown that the intermodulation effects of other gear connected to the main wiring can lead to a marked reduction in the effectiveness of the approach, the submission said. Notches must meet desired aeronautical requirements, Mettrop said. The questions of where harmonics fall and which systems may be effected will need to be studied, Mettrop said.

ITU-R work on a draft report on PLT over 80 MHz “worries administrations,” Liebler said. The work covers frequencies between 80 and 470 MHz, his presentation said. The report may be up for approval this week, Liebler said. Some industry specifications, although not standards in ITU-T or IEEE, appear to be in development for PLT systems above 80 MHz, he said.